1. Field of the Invention
The present invention relates to a plasma enhanced CVD apparatus having a plasma generating electrode in its processing chamber and a process for using it. The present invention further relates to an apparatus for dry etching having a plasma generating electrode in its processing chamber, and a process for using it.
2. Description of the Related Art
Plasma enhanced CVD is a thin film deposition method in which a film is deposited on a substrate by the chemical reaction of source gases using plasma. Plasma enhanced CVD has been widely applied to various thin film deposition processes, e.g., semiconductor IC devices, superconductive devices, various electronic devices, metal films comprising various sensors, semiconductor films, insulation films, photoconductor films, barrier films, and adhesion films. In addition, dry etching is a widely used method for etching such thin films by the chemical reaction of an etching source gas using plasma. In recent years, low-pressure, high-density plasma has attracted the attention of semiconductor engineers in such plasma processing methods. Low-pressure, high-density plasma enables novel processing which has not been realized, and improves processing efficiency.
Prior art will be explained using a plasma enhanced CVD apparatus as an example below. In general, a plasma generating electrode is used to generate plasma in a processing chamber and a radio frequency power is applied to the plasma generating electrode. Plasma generating electrodes are classified as either capacitively coupling types or inductively coupling types, or from a different viewpoint, as external electrode types each having an electrode outside its processing chamber, and internal electrode types each having an electrode inside its processing chamber. Among them, capacitively coupling and internal electrode-type parallel plate plasma enhanced CVD apparatus have been most widely used.
In a parallel plate plasma enhanced CVD apparatus, two electrodes are oppositely provided to each other so as to apply radio frequency power, low frequency power, direct current power, and time-modulated powers thereof to one of them, and to ground the other. Another electrode may be grounded through a capacitor, coil (inductor), or a combination of the capacitor and coil. These parallel plate electrodes are provided to generate and sustain plasma by the interaction caused by collisions between charged particles and between charged particles and the two electrodes after accelerating charged particles by means of an electrostatic field between the two electrodes. The parallel plate plasma enhanced CVD apparatus can hardly generate and sustain plasma under a pressure of 100 mtorr or less. Thus, low-pressure, high-density plasma cannot be generated in such an apparatus.
Inductively coupling types of plasma generating methods have been widely used to generate low-pressure, high-density plasma, as described in, for example, "Novel Development in Low-Pressure, High-Density Plasma" by Hideo Sugai (Applied Physics, Vol. 63, No. 6, pp. 559-567, (1994)). In the inductively coupling-type apparatus, plasma is generated and sustained by the electromagnetic induction caused by current variance of a plasma generating antenna. That is, the plasma is generated and sustained by the interaction between electromagnetic waves and charged particles. Thus, this type can provide low-pressure, high-density plasma since it can generate and sustain plasma even under a pressure of 100 mtorr or less.
In the inductively coupling types, external antenna types have been widely used, wherein a plasma generating antenna is provided outside the processing chamber. In detail, a coil or deformed loop plasma generating antenna is provided around the outside of the discharge chamber, which is made of dielectric materials, to generate the low-pressure, high-density plasma. However, such external antenna types have a drawback. When a film having relatively high conductivity, such as a conductive film or a semiconductive film (hereinafter "conductive film"), is prepared, some of the conductive film is deposited on the inner wall of the dielectric discharge chamber so that electromagnetic waves radiated from the plasma generating antenna provided around the discharge chamber are shielded by the conductive film deposited on the inner wall. Such deposition often causes unstable plasma in the discharge chamber or sometimes causes a failure in plasma generation. Accordingly, the inner wall of the discharge chamber must be frequently cleaned when a conductive film is deposited on a substrate with an external antenna-type plasma generating apparatus.
A method in which an inductively coupling-type antenna is placed inside the processing chamber (hereinafter "internal antenna type") is known as the method compensating for the drawback of the external antenna type, as described in "Hideo Sugai, Kenji Nakamura, Keiji Suzuki: Japanese Journal of Applied Physics Vol. 33(1994) pp. 2189-2193", as well as the above Sugai's article. A sputtering apparatus using such an internal antenna is disclosed in Japanese Laid-Open Patent No. 7-18433.
In the internal antenna-type plasma generating apparatus disclosed in the above article by Sugai et al., an antenna comprising substantially a loop coil of one-turn is provided inside the processing chamber. One terminal of the antenna is connected to a radio frequency power, and the other terminal is grounded. The antenna surface is covered with a dielectric so as to stabilize the plasma. When a conductive film is deposited on a substrate with such a plasma generation apparatus, the following problems will occur. A conductive film deposits on the antenna surface when the conductive film is deposited on the substrate by plasma enhanced CVD. Further, when a metal substrate is etched by dry etching, gaseous metal compounds adhere to the antenna surface and deposit on the antenna surface as a metal film. After the conductive film deposits on the antenna surface covered with a dielectric, the plasma generating state changes with the progress of the substrate processing. Thus, the reproducibility of the substrate processing is lost after a long time batch processing of the substrate. Further, the plasma is unstably generated due to a decreased effect of the dielectric cover. Thus, the antenna surface must be frequently cleaned.
In the plasma generating apparatus disclosed in the aforementioned article by Sugai, a negative direct current bias voltage is induced on the surface of the dielectric cover of the antenna by means of a radio frequency power applied to the antenna. A potential difference between the direct current bias voltage and the plasma potential accelerates positive ions to an extent that the positive ions impinge the dielectric cover on the antenna surface to sputter the dielectric cover. As a result, when such a plasma generating apparatus is used for film deposition, the deposited film may be contaminated with materials from the dielectric cover so it is difficult to deposit a highly pure film.
When the dielectric cover is not provided on the antenna surface in the plasma generating apparatus in Sugai et al., although the above-mentioned problems do not occur, other problems will occur as follows. Since one end of the antenna is grounded so as to pass through a direct current, no direct current bias potential occurs in the antenna, but the antenna potential symmetrically varies between positive and negative with time from the ground potential as the standard due to the radio frequency power applied to the antenna. Charged particles such as electrons and positive ions flow into the antenna due to the variability of the antenna potential with time. Since the mass of electrons is extremely smaller than those of positive ions, electrons have a higher kinetic energy in the electric field. Thus a much greater amount of electrons flows into the antenna than positive ions. On the other hand, since no direct current bias potential occurs in the antenna, the plasma potential necessarily shifts to a positive potential side so that the overall charge of charged particles flowing into the antenna is balanced. The electric field increases between the inner wall of the processing chamber and the plasma, and thus the positive ions are further accelerated toward the inner wall. As a result, a larger amount of secondary electrons are generated by the collision of accelerated positive ions with the processing chamber, and local continuous self-discharge occurs in any place of the inner wall. The inner wall is heated by the continuous discharge, resulting in hot cathode arc discharge. In such an arc discharge mode, a large current flows between the plasma and the inner wall of the processing chamber. Although the space potential in the plasma decreases thereby to temporarily cease the continuous discharge, the space potential in the plasma increases again to cause the continuous discharge between the plasma and the inner wall. In such a way, since the space potential in the plasma periodically and significantly varies, stable plasma cannot be achieved. Further, because the inner wall of the processing chamber is locally overheated by the hot cathode arc discharge, the metal material comprising the processing chamber evaporates to result in the contamination of the processed substrate. When no dielectric cover is provided as described above, the electron density in the plasma is remarkably low compared to the case with a dielectric cover even if the input power is increased. Thus, low-pressure, high-density plasma cannot be achieved by such a method.
In the above sputtering apparatus in Japanese Laid-Open Patent No. 7-18433, a loop antenna of one-turn is provided inside the processing chamber, a terminal of the antenna connects to the radio frequency power and the bias direct current power, and another terminal is grounded through a direct current-blocking capacitor. The antenna itself is used as the target material of the sputtering apparatus. If regarding this apparatus as a plasma generating apparatus and comparing this with the above apparatus by Sugai, there are two differences between them. In the former apparatus no dielectric cover is used for the antenna and one terminal of the antenna is grounded through a capacitor so as not to cause direct current to flow. As a result of such differences, the problems of the apparatus by Sugai are solved in the former apparatus.
However, the present inventors found the following problems when a film is deposited on a substrate by plasma enhanced CVD using the plasma generating apparatus disclosed in Japanese Laid-Open Patent No. 7-18433. That is, in that apparatus, a high bias direct current is applied to the antenna for sputtering the antenna. The film deposition by plasma enhanced CVD using such a high bias direct current causes an excessive sputtering effect. Thus, excellent conformal step coverage of fine contact holes inherent in CVD cannot be achieved. Further, the antenna cannot be used for a long time period due to etching prompted by sputtering. When the direct current bias power and the direct current-blocking capacitor are removed from this apparatus in order to reduce the sputtering effects, other new problems occur, i.e., discharge is unstable and low-pressure, high-density plasma cannot be achieved.
Japanese Unexamined Patent Publication No. 7-254500 discloses a plasma processing device having a plasma generating coil. The position of the plasma generating coil is adjustable. In addition, the surface of the plasma generating coil may be covered with an insulating member, or the plasma generating coil may be formed from a pipe to allow a heating medium to pass therethrough.